Mercury dosage device

ABSTRACT

The mercury dosage device consists of a supporting tube in a holder and a capillary tube fitted inside this supporting tube and in which the upper end of the capillary tube has been connected to means for producing combined suction and blowing action. The magnitude of the dose is determined by the position of the lower end of a stem movable longitudinally within the capillary tube. The outer diameter of the stem is smaller than the inner diameter of the capillary tube in such amount that the suction and blowing effect on the mercury is easily produced but that the mercury cannot enter the space between the stem and the capillary tube.

United States Patent Airola et al.

MERCURY DOSAGE DEVICE lnventors: Aito Kasimir Airola; Martti Kaarlo Johannes Saarinen, both of Helsinki, Finland Assignee: 0y Airam Ab, Helsinki, Finland Filed: Apr. 13, 1970 Appl. No.: 27,599

Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 3,203,455 8/1965 l-lorabin ..14l/329 Primary Examiner-Houston S. Bell, Jr. Attorney-Jesse D. Reingold, Ralph E. Bucknam, Robert R. Strack and Henry A. Marzullo, Jr.

[57] ABSTRACT The mercury dosage device consists of a supporting tube in a holder and a capillary tube fitted inside this supporting tube and in which the upper end of the capillary tube has been connected to means for producing combined suction and blowing action. The magnitude of the dose is determined by the position of the lower end of a stem movable longitudinally within the capillary tube. The outer diameter of the stem is smaller than the inner diameter of the capillary tube in such amount that the suction and blowing effect on the mercury is easily produced but that the mercury cannot enter the space between the stem and the capillary tube.

7 Claims, 4 Drawing Figures Patented March 21, 1972 2 Sheets-Sheet 1 Patented March 21, 1972 2 Sheets-Sheet 2 MERCURY DOSAGE DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mercury dosage device for enclosing a predetermined quantity of mercury in the discharge tubes of high-pressure gas discharge lamps.

2. Background of the Invention In high-pressure gas discharge lamps in the discharge tubes of which mercury constitutes the functioning metal vapor either by itself or in combination with other metal vapors, it is necessary to enclose in the discharge tube a predetermined quantity of mercury with as minimal deviations from the desired quantity as possible. This is because in a functioning discharge tube normally all the mercury is in vaporized condition and the density of the vapor in this space decisively determines the characteristics which a discharge tube, dimensioned in a given way, will have and in particular what will be its arc voltage. The arc voltage is a characteristic quantity of the discharge tube and it is required to be within given limits in order that the lamp might be usable.

The quantity of mercury to be introduced into the discharge tube of the most commonly used high-pressure gas discharge lamps, such as high-pressure mercury lamps and mixed light lamps, is usually in the range of l-l50 mg. or in volume units, correspondingly, in the range of about 0.74-1] mm, the quantity to be placed into each discharge tube depending on the volume of the discharge tube. The higher the power rating of the discharge tube, the larger is usually its volume or capacity, because one attempts to keep the power loading, or the power per unit surface area of the tube, approximately the same in all cases. On the other hand, the density of the mercury vapor should always be in the same order of magnitude, whence follows that the mercury dose is the larger the larger the volume of the discharge tube. Even between discharge tubes with equivalent nominal dimensions there may be variations in volume, owing to variations in inner diameter of the tube blanks. These variations are taken into account when the mercury dose is fixed.

It is required that the magnitude of the mercury dose may be conveniently and accurately adjusted:

I. in greater steps, individually for each type of discharge tube,

2. by smaller steps, consistent with the different volumes of one and the same type of discharge tube.

It is known in prior art to employ, for the purpose of achieving the desired mercury dose, depressions made in a piece of metal and which have a capacity appropriate for the dose in question. The depression is at first brought into contact with a mercury storage so that the depression is filled with mercury. The depression is then disconnected from the mercury storage, and suitable arrangements are brought into play to detach the dose from the depression and to make it fall through the exhaust tube of the discharge tube into the discharge tube. Dosage devices operating according to this principle have been disclosed, e.g., in the U.S. Pat. No. 3,348,588 and the German Pat. No. 1,014,228. A serious drawback with dosage devices of this kind is that a peculiar depression is required for each dose, whereby especially adjustment of the dose by small steps becomes highly awkward.

It is also previously known to use for achievement of a given dose, a thin capillary tube, the length of the mercury column produced in this tube determining the magnitude of the dose. In dosage devices of prior art operating according to this principle the capillary tube contains a longitudinally movable piston. Dosage is accomplished with the aid of this device as follows. The piston is pushed to be flush with the tip of the tube, the tip is brought into contact with the mercury storage, and the piston is retracted through a predetermined distance consistent with the magnitude of the dose, whereby the space preempted by the piston is filled by mercury. The tip is removed from contact with the mercury storage, the piston is once more pushed up to the tip, and the detached mercury dose is conducted by suitable arrangements through the exhaust tube of the discharge tube into the discharge tube. Mercury dosage devices of this kind have been presented, e.g., in the U.S. Pat. No. 3,357,600 and in the book: Dr. W. Elenbaas, High Pressure Mercury Vapor Lamps," Philips Technische Bibliothek 1965, p. I24. The drawbacks of the device just described include the fact that the piston must fit comparatively tightly against the inner surface of the capillary tube and that the movement of the piston in connection of every dosage operation tends to cause abrasion both of the piston surface and of the inner tube surface, which may have the consequence that the mercury dose corresponding to a given length of the column will change and also that the tightness, which is important for proper operation, is impaired.

SUMMARY OF THE INVENTION The mercury dosage device according to the invention comprises a holder carrying a bracing tube. A capillary tube is placed inside the bracing tube and the upper end of the capillary tube is connected to means for producing combined suction and blowing action on the mercury in the capillary tube. A stem is reciprocably movable within the capillary tube and has an outer diameter which is smaller than the inner diameter of the capillary tube to facilitate the production of the suction and blowing action on the mercury dosage the magnitude of which is determined by the position of the lower end of the stem without enabling the mercury to enter the space between the stem and the capillary tube. There is also provided means for moving the stem inside the capillary tube.

The present invention thus makes use of a thin capillary tube for the purpose of achieving a mercury dose of desired magnitude. However, the piston has been replaced with a stem which does not fit tightly against the inner surface of the tube, instead of which such an amount of play has been left that air can freely move in the space between the stem and the inner surface of the tube. On the other hand the gap is small enough, especially at the end of the stem, to prevent the mercury, owing to surface tension forces, from entering the said gap.

According to the invention there is provided a mercury dosage device which is highly accurate and convenient in use.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, one embodiment of the invention is presented by way of illustration, with reference to the attached drawings, in which FIG. 1 shows the dosage device in longitudinal section,

FIG. 2 shows the capillary tube, partly in section,

FIG. 3 shows the stem, and

FIG. 4 presents the appliance for operating the dosage device.

DESCRIPTION OF THE PREFERRED EMBODIMENT Operation A suitable adjusting implement is used to place the stem at such a point that the volume of the space between the end face of the stem and the tip of the tube equals the volume of the desired mercury dose. The tip of the tube is dipped into mercury in a container below its surface, and with the aid of a suitable pumping device an under-pressure is produced within the tube which is sufficient to raise a mercury column up to the end of the stern but which is not high enough in addition to overcome the surface tension forces and to draw mercury in between the stem and the inner surface of the tube. Continuing to maintain the under-pressure, the connection with the mercury storage is broken and the tip of the capillary tube is introduced into the exhaust tube of the discharge tube. The pumping device is operated to replace the under-pressure by pressure higher than atmospheric, whereby the mercury dose in the capillary tube is expelled and blown into the discharge tube.

It is thus understood that the stem will only move in the capillary tube when the magnitude of the dose is changed, and

it has no or only very slight contact with the inner surface of the tube, whereby no substantial wear or abrasion takes place.

A dosage device according to the present invention has been found to function with very high accuracy, the dispersion of the weights of doses obtained with one and the same stem setting being 10.5 percent as a rule. It is thus evident that the device is well appropriate even for highly exacting dosage work.

Construction Referring to FIG. 1, the upper end of the supporting tube 2 has been fixed in a bore in the body 1 of the device. Inside the tube 2 of the capillary tube 11 has been hermetically fixed with the aid of suitable cement, the lower end of capillary tube 11 projecting a few millimeters from the end of the tube. To the body 1 the sleeve 6 has been attached by threads, part of the inner surface of this sleeve being threaded. The adjusting screw 4, which enters the sleeve, has a mating thread, and to its upper end a mantle 3 embracing the sleeve has been fixed. To the lower end of the adjusting screw the upper end of the stem 5 extending into the tube 2 and further into the capillary tube 11 has been fixed. Rotation of the adjusting screw 4 causes the adjusting screw-mantle-stem combination to move longitudinally with reference to the device, whereby the height of the stem in the capillary tube can be accurately adjusted in accordance with the micrometer principle. The outer surface of the sleeve has been provided with a scale indicating turns, and the edge of the mantle has been provided with a scale dividing the circumference, e.g., into equal divisions. To the body 1 also the air pipe 12 has been fixed, which is in flow connection with the capillary tube 11. In order that it might be possible to maintain, through the air pipe 12 connected to an air pump an under-pressure or an overpressure in the capillary tube, it is necessary to seal the combination hermetically. For this reason the stem 5 passes through a rubber packing 7 in the stuffing box 9.

In FIG. 2 the design of the supporting tube-capillary tube assembly has been displayed in greater detail. The outer diameter of the supporting tube 2 is small enough, e.g., 1.3 mm., to enable it to be introduced into the exhaust tube of the discharge tube without difficulty, and its length is great enough to enable its tip to be pushed all the way into the discharge tube. By this means potential sticking of the mercury to the wall of the exhaust tube is prevented. The tip 13 of the capillary tube 11 has been slightly narrowed in order that the detached mercury column might be better held in the tube.

From FIG. 3 the shape of the stem 5 can be seen. The stem is a rod of circular cross section, of which a part 14 ofsuitable length has been ground to be flat on one side in the interest of reduced resistance to air flow. However, a portion 15, about 2 mm. in length, at the lower end of the stem has not been so ground in order to stop the ascent of the mercury. The diameter of this portion is slightly smaller than the inner diameter of the capillary tube 11. If the inner capillary diameter is, for instance, 0.5 mm., the said portion 15 of the stem has a diameter ofabout 0.48 mm.

In FIG. 4 one embodiment of the appliance for operating the dosage device has been shown. It comprises the following essential components; a tubular holder 17 for the dosage device fixed to the housing 16, a mercury storage container 18 with displacement mechanism 19, an air pump 20, and a vertically reciprocable slide 21 with counterweight 22. The holder 17 furthermore carries a longitudinally freely movable protective tube 23. The air pump comprises a mercury reservoir (not visible) and a flexible tube 24 connecting an outlet at the lower end of the mercury reservoir to the air pipe 12. The slide 21 has been connected with the counterweight 22 by a wire 25 passing over a pulley 26 journaled to be freely rotatable.

Operation The operating appliance functions as follows. At commencement of operation the slide 21 is in its upper position. When the slide 21 is moved downwardly, the spring-loaded switching tongue 27 forces the arm 28 of the displacement mechanism 19 of the storage container 18 over to the left side of the guide rail 29. This causes the displacement mechanism 19 to turn around the axes 30, whereby the storage container 18 is moved into position under the dosage device so that the tip of the dosage device is dipped into the mercury in the storage container. In the further course of downward move ment of the slide the rail 29 keeps the storage container 18 stationary, and the descent of the mercury reservoir attached to the slide produces an under-pressure in the air pipe 12, whereby a mercury column ascends from the storage container into the capillary tube, as has been described above. When the arm 28 has cleared the upper end of the rail 29, it returns to the right side of the rail, and the storage container 18 returns to its initial position. The dosage device is now prepared for mercury dosage. The discharge tube is placed in dosage position and the slide 21 is raised. The simultaneous ascent of the mercury reservoir causes the under-pressure in the air pipe 12 to decrease, and when the slide reaches its original position, the inertial movement of the mercury produces in the air pipe 12 a small momentary overpressure, which expels the mercury from the capillary tube in the form of one single droplet. In its further ascent the arm 28 causes the switching tongue 27 to turn, which is thus enabled to pass the arm 28, which remains in its initial position. The operating appliance is now ready for another dosage cycle.

A suitable height of under-pressure has been found to be that of about -200 mm. Hg, in which instance the slide travel is about 25 cm.

We claim:

1. A method of delivering measured quantities of mercury comprising providing a capillary tube and a stem slidable therein wherein the outer diameter of said stem is less than the inner diameter of said capillary tube, dipping the lower end of said capillary tube into a pool of mercury, applying a pressure below atmospheric to an upper longitudinal portion of the space between said stem and capillary tube, passing air from a lower longitudinal portion of said capillary tube through the space between the stem and capillary tube to said upper longitudinal portion as said stem remains stationary, drawing in a column of mercury into said lower longitudinal portion of said capillary tube below the longitudinal end of said capillary tube as air passes between said stationary stem and capillary tube and mercury is precluded from passing therebetween, removing said capillary tube from said pool of mercury, applying a pressure above atmospheric to said upper longitudinal portion of the space between said stem and capillary tube, passing said air between said stem and capillary tube to expel said column of mercury from said capillary tube or said stem remains in fixed positions, and adjusting the longitudinal position of said stem in said capillary tube to predetermine the amount of mercury to be drawn into said capillary tube.

2. A mercury dosage device for delivering measured quantities of mercury comprising a holder, a supporting tube carried by the holder, a capillary tube mounted within said holder, the lower end of said capillary tube being adapted to be dipped into a storage container of mercury during the filling of the device, a stem slidably mounted within said capillary tube into arbitrary fixed positions, said stern having an outer diameter smaller than the inner diameter of said capillary tube, operable means connected to the upper end of the capillary tube for producing a pressure below atmospheric and a pressure above atmospheric within said capillary tube, said stem outer diameter and said capillary tube inner diameter being such that air can pass between the stem and capillary tube to draw in a column of mercury in the lower end portions of said capillary tube below said stem without being drawn into the space between said stem and capillary tube when said operable means applies a pressure below atmospheric to said capillary tube and to expel said column of mercury from said capillary tube when said operable means applies a pressure greater than atmospheric and means operationally connected to the stem for longitudinally moving said stem within said capillary tube to predetermine the amount of mercury drawn into said capillary tube.

3. A mercury dosage device according to claim 2 wherein said stem has a flat portion for reducing the resistance to air flow between said stem and capillary tube, said flat portion being spaced from the lower end ofsaid stem.

4. A mercury dosage device according to claim 2 wherein the lower terminating end of the capillary tube is provided with a section having a reduced outer diameter.

5, A mercury dosage device according to claim 2 in which said means for moving said stem comprises an adjustment screw movable in the longitudinal direction of the stem and fixed to the upper end of said stem.

6. A mercury dosage device according to claim 2 comprising packing means on said holder above said operable means, said stem being slidably through said packing means, said operable means comprising an air pipe in communication with the capillary tube and also in communication with a pumping unit 7. A mercury dosage device according to claim 6 wherein said pumping unit comprises a mercury column which is raisable and lowerable with the aid of a flexible tube with respect to said holder. 

1. A method of delivering measured quantities of mercury comprising providing a capillary tube and a stem slidable therein wherein the outer diameter of said stem is less than the inner diameter of said capillary tube, dipping the lower end of said capillary tube into a pool of mercury, applying a pressure below atmospheric to an upper longitudinal portion of the space between said stem and capillary tube, passing air from a lower longitudinal portion of said capillary tube through the space between the stem and capillary tube to said upper longitudinal portion as said stem remains stationary, drawing in a column of mercury into said lower longitudinal portion of said capillary tube below the longitudinal end of said capillary tube as air passes between said stationary sTem and capillary tube and mercury is precluded from passing therebetween, removing said capillary tube from said pool of mercury, applying a pressure above atmospheric to said upper longitudinal portion of the space between said stem and capillary tube, passing said air between said stem and capillary tube to expel said column of mercury from said capillary tube or said stem remains in fixed positions, and adjusting the longitudinal position of said stem in said capillary tube to predetermine the amount of mercury to be drawn into said capillary tube.
 2. A mercury dosage device for delivering measured quantities of mercury comprising a holder, a supporting tube carried by the holder, a capillary tube mounted within said holder, the lower end of said capillary tube being adapted to be dipped into a storage container of mercury during the filling of the device, a stem slidably mounted within said capillary tube into arbitrary fixed positions, said stem having an outer diameter smaller than the inner diameter of said capillary tube, operable means connected to the upper end of the capillary tube for producing a pressure below atmospheric and a pressure above atmospheric within said capillary tube, said stem outer diameter and said capillary tube inner diameter being such that air can pass between the stem and capillary tube to draw in a column of mercury in the lower end portions of said capillary tube below said stem without being drawn into the space between said stem and capillary tube when said operable means applies a pressure below atmospheric to said capillary tube and to expel said column of mercury from said capillary tube when said operable means applies a pressure greater than atmospheric and means operationally connected to the stem for longitudinally moving said stem within said capillary tube to predetermine the amount of mercury drawn into said capillary tube.
 3. A mercury dosage device according to claim 2 wherein said stem has a flat portion for reducing the resistance to air flow between said stem and capillary tube, said flat portion being spaced from the lower end of said stem.
 4. A mercury dosage device according to claim 2 wherein the lower terminating end of the capillary tube is provided with a section having a reduced outer diameter.
 5. A mercury dosage device according to claim 2 in which said means for moving said stem comprises an adjustment screw movable in the longitudinal direction of the stem and fixed to the upper end of said stem.
 6. A mercury dosage device according to claim 2 comprising packing means on said holder above said operable means, said stem being slidably through said packing means, said operable means comprising an air pipe in communication with the capillary tube and also in communication with a pumping unit.
 7. A mercury dosage device according to claim 6 wherein said pumping unit comprises a mercury column which is raisable and lowerable with the aid of a flexible tube with respect to said holder. 